Electricity + Control August 2019

ELECTRICAL PROTECTION + SAFETY

they provide a low earth resistance and represent an excellent basis for equipotential bonding. As a medium voltage transformer is also installed in the wind turbine, the earth-termination system must be designed according to international standard IEC 61936-1, which describes all types of earth electrodes. Foundation earth electrodes are defined as the most effective earth electrodes. When working out the dimensions of the earth termination system, it is important to factor in the composition of the surrounding ground and the type of neutral point treatment and the resulting short circuit currents in case of a fault. Moving forward “We believe that South Africa is on the verge of a tremendous increase in the use of renewable wind energy generation.When the green light is given for more investment in the renewables space and the current Draft Integrated Resource Plan for electricity is finalised, companies will want to move quickly with their wind energy production plans. The time for planning is now, and it should be remembered that each wind turbine needs to be earthed properly and individually,” concludes Vögerl.

to, or higher than, the lightning hot spots of north and south America, Asia and northern Australia . “Lightning strikes in South Africa,” says Vögerl, “are in general more frequent than those found in many parts of Europe, where much of the world’s renewable energy technology is developed and implemented. We therefore have more reason to look after our renewable energy equipment than our colleagues in Europe do. It is critically important to protect renewable energy generation equipment in South Africa from lightning strikes. The impact of a lightning strike to an unprotected renewable energy source will necessitate physical repairs or replacement – with the associated costs – and could cause reputational damage.” He highlights that, in some cases, wind turbines are imported into South Africa with the lightning protection equipment already pre-assembled and that DEHN Africa’s work requests relate mostly to the earthing of the turbines. Appropriate earthing for wind turbines In this regard, Vögerl says the earth termination system for onshore wind turbines must provide the following: - Protective earthing, which safely connects electrical equipment to the ground and protects people and property in the event of an electric fault - Functional earthing, which needs to ensure safe and efficient operation of the electrical and electronic equipment - Lightning protection earthing, which must safely conduct the lightning current from the down conductors to the ground. In a white paper on the earth termination of onshore wind turbines DEHN advises that, with regard to lightning protection earthing, it is advantageous to have a single, common earth-termination system for all purposes (medium voltage system, low voltage supply, lightning protection, electromagnetic compatibility, telecommunication and control systems). The white paper notes further that the reinforced concrete foundations of wind turbines should serve as a foundation earth electrode, as

References i

https://mg.co.za/article/2017-05-26- 00-wind-energy-has-much-more- potential-than-expected https://renewablesnow.com/news/ solar-wind-power-are-40-cheaper-than- coal-in-south-africa-csir-543589/ iii https://www.businessinsider.co.za/5- massive-new-renewable-energy- projects-that-transformed-south- africas-landscape-2018-4 iv A Lightning Threat Index for South Africa, Morné Gijben, https://repository. up.ac.za/bitstream/handle/2263/57242/ Gijben_Lightning_2016.pdf?sequence =1&isAllowed=y ii

In South Africa, where many parts of the country have a high lightning ground flash density, it is essential to protect wind turbines from lightning strikes.

Electricity + Control

AUGUST 2019

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